Separation of xylene



:xylene content of the crude xylene.

Patented Feb. 12, 1952 UNITED STATES PATEL 1 KOFFI CE Monsanto ChemicalCompany, .St.;L'ouis, Mm,

a corporation of Delaware No Drawing. Application May 26, 1950, SerialNo. 164,620

7 Claims. 1

The-present invention relates to hydrocarbon recovery, and deals moreparticularly with the separation of para-xylene from technical Xylenefractions.

A'gre'at-deal'of effort has been directed to the provision -of processesfor the isolation of the isomeric xylenes from hydrocarbon fractions'containing the same. Based on the fact that'meta- "xylene is morereadily sulfonate'd than the other xylenes, a number of prior processeshave employed sulfonation procedures, particularly for therecover-yoimeta-xylene.

The difierence known to exist in the ease of hydrolysis of the variousxylenesulfonic acids'has also contributed to theirequent use ofthe-sulfonationtprocedure.

FI'hus,iin'.pri0r art, it was known that the partialfsulfonationof acrude xylene fraotion e. g., byramoderately strong sulfuric'acidunder-conditions preventing complete-sulfonation would dissolve, or'sulfonate, apredominance of the m- The other :xylenes were believed tobe either undissolvedor only-partially. affected under the sameconditions.

It -was also known that Xylenesulfonic acids canbe fracticnallyhydrolyzed to the corresponding Xylenes. For example, in asteam-distillationhydrolysis, m-xylenesulfonic acid was found.tohydrolyze at temperatures of from 125 to I50 .C., paraxylenesulfonicacid at temperatures of from 150 to 170 0., and o-xylenesulfonic acidand thylbenzenesul'fonic acid at above 170 C.

Based on the above, there'have'been devised various methods 'for theseparation of 'theindividual 'xylenes as Well as of the ethylbenzene:present in "technical xylene fractions. The xylene was first "partially-sulfonated, "e. e., by treatmenttvith a"sulfuric"aci'd, o'fsayless'thaniQ'S per cent H2804 concentration, and the unsulfonate'd oilwas separated, "and submitted to complete 40 'sul'fonation, i. e.,treatment with a stronger "sulfuric acid. Separation of the Xylenespresent "inihe 'two dii ferent sulfonic acid fractions "thus obtainedwas then efiected either by selective :hydrolysis, fractionalcrystallization or --a combinati'on' of the two procedures.

Depending upon the individual xylene isomer :desired, the proceduregenerally outlined above has :been somewhat varied. However, the priorartshas :not provided an industrially Ieasible (CLaZGO-s-GZ l) ,12method for ltheasiibstantiallyatotal "recovery of a high gr'adepara-xylene :and wot .-a -=high+grade e'thylbenzen'e isfromztechnical:xyl'ene mixtures.

An object of "the present :invention is to "re- "cover in good yieldstpure or. substantially .Pure para-xy lene from imix'tures thereof withother stylen'es. knother obie'ctirof @the invention .:is to recover-pure .:or substantially aaure ethylhenzene from technical :xylene&fractions containing 'ethylbenzene. Other objects will :be hereinafterdisclosed.

According to the .inventiona'azrecovery of para- "xyl'ene and,'if:desired, of ethylb'enzene fromtcrude xylene, i. e., xylene ifrom.commercial sources 15 -such as coal-tar, cokeovenzdistillates,:petroleum tarbils, etcxis efi ectedzin ib'etterpyieldsthanshave "been -previous'ly attained on :a technical sscale byoperating substantially as follows:

Crude xylene is--dis'til1'e'dto remove a majo'r portion of its-orthoxylene"content to give a hy- 'drocarboniraction" havinga boiling pointof' approx'im'ately 130 C. to '145" "'Cxandmon'ta'ining a predominanceofmeta xylene,fa*lesseriproportion of para-xylene and small "amounts ofethyllbenzenean'd ortho-xyllene. This distilled pro'dnot will bedeferred .tofhereinafteras technical .xylene. LThis hydrocarbon:fraction is.submitted :to partial sulfonation, the .unsul fonated voil.(a) .is separated .from .theqproduct and-the sulfonated -material ..(b).is subjected-to iractional distillastion hydrolysis. -'.Foreruns 'tc):obtainedbytfractional distillation hydrolysis rat etemperatures-of upto 120 C.' are 1addeii toithe unsulfonatedtmaterial (a), intermediatematerial hydrolyzing at from 120 C. to 145 C. and comprisingsubstantially m-xylene is separatedand hydrolysis prod- .uct .(d).ohtained by :hydrolyzing at above 145 C. is alsoadiiedto thewunsulfonatedoil (a). The mixture-- .of nnsu lfonated oil la),.hydrolys'is (foreruns (0) and hydrolysis roduct (d) is thencom-.pletely sulfonated, e. g. by treatment with strong isulfuric acid, i.e., of above 95 per cent .H2SO4 45 concentration. Distillation"hydrolysis 'of :the

-.comple"tely sulfona'ted material yields, at a tem- .perature (if "fromT50" C. "to TTO C. air'ation containing a predominance of para-xyleneand :above 1:7.0" E. :a ifractinn -icontainmg 51a :preiiomi- 50mancemnethylbenzener 3 Briefly, the present process may be outlined asfollows:

Technical xylene partial sulionetlon Suionlc acid (b) iracltionalhydrolysis l 120 C. 125-145 0. 145 C. l oreruns (c) m-Xyilene HydrolysisI on Product (d) Unsulionated 011 (a) [Hydrolysis product (d) ForerunsComplete sulionation Sulionic acid (e) Fractional h l'drolys is 1 150 C.150-170" C. 170C. I mylene cut p-Xylelne cut Etltiylbenzene coolingCrystalline p-xylene the hydrolysis step material coming over at below120 C. consisted essentially of water and paraffinic compounds. Alsounappreciated were the advantages obtainable by a re-sulfonating thehydrolysis product ((7.) along with the unsulfonated oil (a). Contraryto previous practice, we have found that incorporation of the hithertodiscarded foreruns (0) into the material which is to be re-sulfonatedresults in a substantially increased recovery of xylenes, particularlyp-xylene, as well as of ethylbenzene. With respect to p-xylene, ourinvestigations have shown that while re-sulfonation of only theunsulfonated oil (a) results in the recovery of but about 50 per cent ofthe p-xylene present in the xylene mixture, addition of the foreruns (c)to the unsulfonated oil (a), and complete sulfonation of the resultingmixture results in the recovery of about 70 per cent of the p-xylene.Addition to the unsulfonated oil (a) of not only the foreruns (0) butalso the hydrolyzed product ((1) results in the recovery of about 85 percent of the p-xylene. The present process also permits substantiallycomplete recovery of ethylbenzene from technical xylene mixtures.

The invention is further illustrated, but not limited, by the followingexample:

Example A technical xylene fraction having a boiling point of 125 C. to141.7 C. after removal of 191.8 pounds of the above fraction was reactedwith 85 per cent sulfuricacid fora time of 30 minutes at a temperatureof from C. to C. The quantity of acid employed was 2.74 lbs. of 85 percent H2804 per lb. of the fraction.

The unsulfonated oil (a) weighing 67.8 lbs. was separated from thereaction mixture, and the remaining sulfonic-sulfuric acid mixture wasdiluted with water and steam distilled to a temperature of C. There wasthus obtained 18 lbs. of the forerun (c), which was added to theunsulfonated oil (a). Further distillation of the remainder of thesulfonic-sulfuric acid mixture at a temperature of from 120 C. to C.gave 90 lbs. of a fraction consistin predominantly of meta-xylene.Distillation of the residue at a temperature of over 145 C. gave 16 lbs.of a hydrolysis product (d), which was also added to the unsulfonatedoil (a) The 101.8 lbs. of the mixture of unsulfonated oil (a), forerun(c) and hydrolyzed product (d) were then sulfonated completely byreaction with 96 per cent sulfuric acid. The resulting sulfonic-sulfuricacid mixture was then diluted with water and the temperature of thediluted mixture was raised to 145 C. to C. At this temperature there wasobtained a fraction consisting essentially of 40.1 lbs. of meta-xylene.Distillation hydrolysis of the remainder at a temperature of from 150 C.to C. yielded 49.7 lbs. of a fraction containing 44.9 lbs. (90.4 percent) of para-xylene. At over 170 C. there was obtained 12 lbs. of afraction consisting essentially of ethylbenzene.

The fraction distilling at 150 C. to 170 C. and consisting of 90.4 percent para-xylene, 4.0 per cent of meta-xylene and 5.6 per cent oforthoxylene may be used as such for many industrial purposes, or thepara-xylene may be further concentrated by cooling the fraction to minus12 C. whereby the para-xylene solidifies. Filtration of the solidpara-xylene yields 40.1 lbs. of an approximately 98 per cent purepara-xylene.

The above procedure may be somewhat varied, particular with respect tothe composition of the xylene fraction employed in the firstsulfonation.

It has been found that in order to obtain paraxylene of at least 90 percent purity, the ratio of ortho-xylene to para-xylene in the xylenefraction should not be greater than 1:20, and that the purity of thepara-xylene increases with decreasing content of ortho-xylene in thematerial which is to be sulfonated. Thus, careful fractionaldistillation to give a fraction containing only from 0.2 to 0.3 per centof ortho-xylene, instead of the fraction employed for the firstsulfonation in the above example, may yield a para-xylene in the seconddistillation hydrolysis step of approximately 95 per cent purity. Inthis case further concentration by fractional crystallization will beunnecessary for most purposes.

The first sulfonating procedure may also be somewhat varied. The acidneed not be of 85 per cent strength; however, the acid strength and theconditions of time and temperature employed for the sulfonation shouldbe such as to permit only partial sulfonation, for example sulfonationof from, say, 30 per cent to 80 per cent of the xylene fraction,depending upon the metaxylene content of the fraction.

The present process is suitably employed for the recovery of para-Xyleneand of the ethylbenzone from technical xylenes of varying compositionscontaining preponderant quantities of meta-xylene and para-xylenetogether with lesser quantities of ortho-xylene and ethylbenzene.

What I claim is:

1. In a process for the recovery of para-xylene from technical xylene,the steps which include partially sulfonating said xylene, removingunsulfonated oil from the partially sulfonated product, fractionallyhydrolyzing the residue at a temperature of up to 120 C., bringingtogether the hydrolyzed fraction with the unsulfonated oil, completelysulfonating the resulting mixture and fractionally hydrolyzing thecompletely sulfonated material to obtain a predominantlypxylene-containing fraction.

2. In a process for the recovery of para-xylene from technical xylene,the steps which include partially sulfonating said xylene, removingunsulionated oil from the partially sulfonated product, fractionallyhydrolyzing the residue to obtain a first hydrolyzed product boiling ata temperature of up to 120 C. and a second hydrolyzed product boilingabove a temperature of 145 C., 1.:

adding the first and the second hydrolyzed products to said unsulfonatedoil, completely sulfonating the resulting mixture and fractionallyhydrolyzing the completely sulfonated material to obtain a predominantlyp-xylene-containing fracn tion.

3. In a process for the recovery of para-xylene and of ethylbenzene fromtechnical xylene, the steps which include partially sulfonating saidxylene, removing unsulfonated oil from the partially sulfonated product,fractionally hydrolyzing the residue to obtain a hydrolyzed productboiling up to a temperature of 120 C., bringing together the hydrolyzedproduct with the unsulfonated oil, completely sulfonating the resultingmixture, and iractionally hydrolyzing the completely sulfonated materialto obtain a predominantly para-xylene-containing fraction and apredominantly ethylbenzene-containing fraction.

4. In a process for the recovery of para-xylene and of ethylbenzene fromtechnical xylene, the steps which include partially sulfonating saidxylene, removing unsulfonated oil from the partially sulfonated product,fractionally hydrolyzing the residue to obtain a first hydrolyzedproduct boiling at a temperature of up to 120 C. and a second hydrolyzedproduct boiling at a temperature of over 145 0., adding the first andsecond hydrolyzed products to said unsulfonated oil,

completely sulfonating the resulting mixture, and fractionallyhydrolyzing the resulting material to obtain a predominantlypara-xylene-containing fraction and a predominantlyethylbenzene-containing fraction.

5. A process for the recovery of para-xylene and ethylbenzene fromtechnical xylene containing major proportions of meta-xylene and ofpara-xylene and minor proportions of orthoxylene and of ethylbenzenewhich comprises reacting said technical xylene with sulfuric acid underconditions permitting only partial sulfonation of the technical xylene,removing unsulfonated oil from the resulting reaction mixture, dilutingthe residue with water, distilling the diluted material to obtain aforerun boiling up to a temperature of approximately 120 C., anintermediate hydrolysis fraction boiling at a temperature of from 120 C.to 145 C, and another hydrolysis product boiling above 145 0., addingsaid forerun and the last hydrolysis product to the unsulfonated oil,treatingthe resulting mixture with sulfuric acid for a completesulfonation Ill of said mixture, diluting the completely sulfonatedmaterial with water, distilling the diluted material to obtain apredominantly para-xylenecontaining fraction boiling between atemperature of from 150 C. to 170 C. and a predominantlyethylbenzene-containing fraction boiling above 170 C.

6. A process for the recovery of para-xylene and ethylbenzene fromtechnical zylene containing major proportions of meta-xylene and ofpara-xylene and minor proportions of orthoxylene and of ethylbenzenewhich comprises reacting saidtechnical xylene with sulfuric acid underconditions permitting only partial sulfonation of the technical xylene,removing unsulfonated oil from the resulting reaction mixture, dilutingthe residue with water, distilling the diluted material to obtain aforerun boiling up to a temperature of approximately 120 C., anintermediate hydrolysis fraction boiling at a temperature of from 120 C.to 145 C. and another hydrolysis product boiling above 145 0., addingsaid forerun and the last hydrolysis product to the unsulfonated oil,treating the resulting mixture with sulfuric acid for completesulfonation of said mixture, diluting the completely sulfonated materialwith water, distilling the diluted material to obtain a predominantlypara-xylenecontaining fraction boiling between a temperature of from 150C. to 170 C. and a predominantly ethylbenzene-containing fractionboiling above 170 C., cooling the fraction which boils at a temperatureof from 150 C. to170 C. to solidify paraxylene and filtering thesolidified para-xylene from the cooled fraction.

'7. A process for the recovery of para-xylene and ethylbenzene fromtechnical xylene containing major proportions of meta-xylene and ofpara-xylene and minor proportions of orthoxylene and of ethylbenzenewhich comprises reacting said technical xylene with sulfuric acid ofless than per cent H2804 concentration under conditions permitting onlypartial sulfonation of the technical xylene, removing unsulfonated oilfrom the resulting reaction mixture, diluting the residue with water,distilling the diluted material to obtain a forerun boiling up to atemperature of approximately C., an intermediate hydrolysis fractionboiling at a temperature of from 120 C. to C. and another hydrolysisproduct boiling above 145 0., adding said forerun and the lasthydrolysis product to the unsulfonated oil, treating the resultingmixture with sulfuric acid of greater than 95 per cent concentration forcomplete sulfonation of said mixture, diluting the completely sulfonatedmaterial with water, distilling the diluted material to obtain apredominantly para-xylene-containing fraction boiling between atemperature of from C. to C. and a predominantly ethylbenzene-containingfraction boiling above 170 C.

WILLIAM F. YATES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,311,848 Lepers July 29, 19192,282,231 Mattox May 5, 1942 2,511,711 I-Ietzner et al. June 13, 19502,519,336 Beach Aug. 22, 1950

1. IN A PROCESS OF THE RECOVERY OF PARA-XYLENE FROM TECHNICAL XYLENE,THE STEPS WHICH INCLUDE PARTIALLY SULFONATING SAID XYLENE, REMOVINGUNSULFONATED OIL FROM THE PARTIALLY SULFONATED PRODUCT, FRACTIONALLYHYDROLYZING THE RESIDUE AT A TEMPERATURE OF UP TO 120* C., BRINGINGTOGETHER THE HYDROLYZED FRACTION WITH THE UNSULFONATED OIL, COMPLETELYSULFONATING THE RESULTING MIXTURE AND FRACTIONALLY HYDROLYZING THECOMPLETELY SULFONATED MATERIAL TO OBTAIN A PREDOMINATNTLYPXYLENE-CONTAINING FRACTION.